This invention relates to corrosion inhibitors primarily, but not exclusively, for use with oil well exploration and development pipelines. The invention relates more specifically to use with xe2x80x98coiled tubingxe2x80x99.
The coiled tubing is typically a flexible steel pipe several kilometres in length with an internal diameter in the region of 5 centimeters. It is supplied and used by sub-contractors who provide such services as xe2x80x98well conditioningxe2x80x99 and inspection to oil production and exploration companies. While carrying out these operations various solutions may be circulated through the coiled tubing, for example xe2x80x98scale dissolverxe2x80x99. While the exact compositions of these solutions are closely guarded secrets, each sub-contractor having their own proprietary blends. It is known that most are based on hydrochloric acid or other such corrosive compounds.
On completion of a contract, to prevent corrosion of pipes by any residual scale dissolvers etc, the pipes are rinsed. A typical procedure for rinsing and cleaning the coiled tubing is to purge with nitrogen, rinse with a caustic solution to neutralise any acidic residues in an attempt to minimise corrosion, then purge again with nitrogen. Most of the corrosion occurs between jobs.
Prior to committing a coiled tube to further contracts it is inspected and pressure tested. Although pipes are rinsed after a period of sustained use, almost invariably heavy internal corrosion caused by use of acid conditioning agents, and from bi-products of the rinsing process means that before pressure testing there is a need to clean the tube by xe2x80x98acid picklingxe2x80x99 to remove the corroded surface. This continuous cycle of corrosion and cleaning results in the walls of the tubing becoming thinned. The thinned walls increase the likelihood of pin holes forming and therefore leaks in the tubing during use, resulting in expensive downtime for the sub-contractor.
Although the need to find a solution to the problem of internal corrosion of coiled tubing has been recognised by the sub-contract companies, so far they have made little progress. The addition of caustic solution to neutralise the acids has proved ineffective, and may actually be accelerating the corrosion by forming sodium or potassium chlorides in situ which are known to be highly corrosive to steel. Another avenue that has been explored is the application of dry film resin bonded coatings to the internal surface of the tubing, however this has proved to be expensive and difficult to apply, therefore limiting it""s use.
The present invention relates to a method of preventing corrosion in pipelines comprising draining pipeline of all residual compounds, blowing through with nitrogen and rinsing with a rinsing agent, characterised in that the rising agent is corrosion inhibiting. The rinsing agent cleans out and neutralises any acid residues and leaves a corrosion inhibiting oily film. Preferably, the pipeline is rinsed with the rinsing agent immediately after use.
Also according to the present invention, a pacifier corrosion inhibiting rinsing agent comprises an emulsifable oil and passifier materials.
In a preferred embodiment of the present invention, the corrosion inhibiting rinsing agent is biodegradable and consists of a mixture of one or more vegetable oil derived base oils, one or more emulsifiers, and one or more corrosion inhibitors.
As the product would be for use offshore, it is necessary for the corrosion inhibiting rinsing agent to be biodegradable, this would then prevent any serious harm to aquatic organisms in the event of spillage
After the use of a section of coiled tubing in a process such as well conditioning, all residual conditioning solutions are drained from the pipeline and the pipeline removed from the well assembly. The pipeline is then blown through with nitrogen and then immediately rinsed with a corrosion inhibiting rinsing agent of the present invention. This agent has the effect of neutralising any residual acidic solutions which cause corrosion of the pipeline due to the neutralising effect of the triethanolamine. Once this rinsing solution has been flushed through the pipeline the oily nature of the composition, due to the vegetable oil and methyl ester content, xe2x80x98plates outxe2x80x99 a protective film which adheres to the inner surface of the tube. This effect is enhanced by the use a mixed anionic/non-ionic emulsifier system which results in the oil droplets of the emulsion becoming larger, more unstable and therefore more likely to xe2x80x98plate outxe2x80x99 as the acidity increases.
The prior art is simply the use of a caustic rinse on the tubing, no other system to neutralise or prevent further corrosion is in use.
The corrosion inhibiting rinsing agents of the invention can be used either by flushing through the pipe as a dilute solution or by introducing and passing a xe2x80x9cplugxe2x80x9d of neat rinsing agent through the pipe.